Biological fluids, such as blood, spinal fluid, cell cultures and urine, are frequently examined microscopically to determine the presence or concentration of suspended particulate matter. For many years, a drop of the liquid specimen was first placed on a flat transparent microscope slide. A thin flat transparent cover slip was then placed over the specimen. More recently unitary plastic slides as shown in U.S. Pat. No. 4,637,693 have become available. Such unitary slides include at least one examination chamber formed between integral base and cover plates. A liquid specimen is drawn by capillation into the chamber from a drop placed adjacent thereto.
To accurately determine the concentration of suspended particles or cells in a liquid specimen, several parameters must be either measured or maintained at constant values. These parameters include the interior dimensions which determine the volume of the examination chamber and the volume of fluid from which the sample is taken. In urinalysis procedures the sample is taken at a standard volume of 12 ml. The 12 ml. sample is centrifuged and 11 ml. are decanted. The sediment is resuspended in the remaining 1 ml. to provide a 12 to 1 concentration of the particulate. This procedure is facilitated by use of the pipette described in Mitchell U.S. Pat. No. 4,563,332.
Unitary plastic slides as described in U.S. Pat. No. 4,637,693 have examination chamber roofs spaced a predetermined distance from the chamber floors. With such slides the only remaining dimension required to determine the volume of specimen liquid under examination is the lateral dimension of the field of view of the examining instrument, e.g., a microscope. This lateral dimension varies depending on magnification and the optics used in the instrument. Therefore, standardization requires either that all microscopes or the like have the same field of view or that the differences in fields of view must be calculated and factored into the various counts of suspended particulate matter.
Pursuant to this invention a grid system is defined on the floor of a slide examination chamber, thus eliminating the need to consider the lateral extent of the field of view of the examining instrument. Such a grid system may be provided on the examination chamber floor of a slide which is utilized with a separate cover slip or of unitary slide having a permanently affixed cover plate as shown for example in U.S. Pat. No. 4,637,693.
Such slides are made of transparent optical quality plastic. The grid must either be machined or scribed onto the chamber floor after the slide is molded or formed from a pattern incorporated into the mold. This invention provides molds and molding procedures useful to incorporate a grid pattern into an examination chamber floor during the molding process.
Many applications, e.g., urinalysis procedures, require magnification of the order of 400 times. At this magnification the diameter of the fields of view vary from about 0.33 millimeters (mm) to 0.50 mm. Grid systems with narrow defining lines, e.g., 0.025 mm in width, separated by less than half a millimeter are required. Otherwise, portions of the grid perimeter will extend beyond the field of view requiring adjustments to the microscope or other magnification instrument, thus effectively defeating the purpose of the grid.
Pursuant to this invention fine patterns such as grids are provided on plastic optical components, specifically urinalysis slides, for use at magnification of from about 10.times. to about 1500.times.. A magnification range of from about 350.times. to about 450.times. is appropriate for most purposes. Pattern line widths of from about 0.005 to about 0.05 mm and pattern line spacings of from about 0.06 mm to about 9 mm accommodate such magnification ranges.